Codebase Orientation Walkthrough overview

Delivers a structured deep-dive into the codebase architecture for newly onboarded engineers — walking through the repository layout and module boundaries, explaining the build system and CI pipeline from first principles, demonstrating local development environment setup with smoke tests, reviewing key architectural decisions and their ADR documentation, tracing a representative request end-to-end through the system layers, and pairing on a small starter task that touches each layer. Produces onboarding checklists with completion timestamps, architecture map annotations, and new-hire feedback for documentation improvement. Excludes role-specific training.